It is necessary to perform many tasks down hole of a completed tubing string. These tasks ordinarily must be performed at specified elevations. In many instances, it is difficult if not impossible to determine the elevation at which a job must be performed. The device of the present invention is a collar locator which enables a wire line operator to determine the elevation at which a particular job must be performed. The device of the present invention particularly enables the operator to run the tool through the well to the bottom of the well. It is useful in a perfectly vertical wells and in slant holes also. Moreover, it preferably operates on the return trip under tension. The downward trip where the tool is dropped into the well is some what problematic inasmuch as the wire line may develop slack in the cable and may not travel smoothly from collar to collar on the gravity ball. Thus, the device is particularly useful in that it can be dropped to the bottom of a tubing string. It is then triggered into a state of readiness by use of a jar device run on the wire line with the tool. At this juncture, it is then ready to operate and is pulled from the well with tension on the wire line. When it is pulled, accurate measurements are derived from the wire line that is retrieved at the surface.
The tension on the wire line is easily monitored and the amount of pull required to retrieve the tool varies each time the tool passes through a collar. This determines the number of collars passed to a specified location. This will determine the distance of a specified location from the bottom of the well and will enable the performance of a specified job or task at that location.